Perfluoropolyethers have long been recognized for their outstanding thermal properties and wide liquid ranges. Perfluoropolyethers are normally made either from anionic polymerization of perfluoro epoxide or from the UV photolysis of tetrafluoroethylene or hexafluoropropylene in an inert solvent in the presence of oxygen. Both of these processes produce relatively expensive perfluoropolyethers.
The preparation of perfluoropolyethers by anionic polymerization of perfluoro epoxides first involves the oxidation of a perfluoro olefin to a perfluoro epoxide, followed by anionic polymerization of the epoxide to an acyl fluoride terminated perfluoropolyether and conversion of the acyl fluoride end groups to unreactive end groups by decarboxylation reactions or chain coupling photolytic decarboxylation reactions. The inability to form very high molecular weight polymers, the lack of stability of many perfluoro epoxides, and the extreme difficulty encountered when attempting to polymerize substituted perfluoro epoxides have been cited as drawbacks to this method. In addition, anionic polymerization of perfluoro epoxides does not lend itself well to the manufacture of perfluoro copolymers since perfluoro epoxides vary widely in reactivity.
An alternate synthetic method for the production of perfluoropolyethers involves the UV photolysis of tetrafluoroethylene and/or hexfluoropropylene in an inert solvent in the presence of oxygen. This multistep process yields an acyl fluoride terminated polymer containing --CF.sub.2 O--, --CF.sub.2 --CF.sub.2 --CF.sub.2 --CF.sub.2 --, --CF.sub.2 --CF.sub.2 --O--, and --CF(CF.sub.3)--CF.sub.2 --O--repeating units as well as unstable peroxidic oxygen linkages (--CF.sub.2 --O--O--CF.sub.2 --). Treatment of the polymer at high temperatures and with fluorine gas gives a stable polymer containing perfluoroalkyl end groups. See U.S. Pat. Nos. 3,665,041; 3,847,978; 3,770,792; and 3,715,378.
Although this process can produce copolymers, the process is completely random with little control over the kinds and number of repeating units. Undesirable linkages such as the peroxidic oxygen and the poly(difluoromethylene) portions of the polymer are unavoidable. These groups can give the polymer undesirable properties for many applications. The formation of by-products and the need for fairly exotic solvents add significantly to the production costs of the polymer.
In contrast to the above-described process, direct fluorination of hydrocarbon ethers allows one to select among many more structural forms of ethers because synthetic methods for production of a wide variety of hydrocarbon ethers. The direct fluorination of hydrocarbon ethers using the LaMar process offers an economical, versatile route to production of perfluoropolyethers.